The present invention relates generally to improvements in electronic shelf label (ESL) systems used in transaction establishments. More specifically, the present invention relates to advantageous aspects of a wireless ESL communication system having multiple transmit antennae.
ESL systems typically include a plurality of ESLs for each merchandise item in a store. ESLs display the price of corresponding merchandise items on store shelves and are typically attached to a rail along the leading edge of the shelves. A store may contain thousands of ESLs to display the prices of the merchandise items. The ESLs are coupled to a central server where information about the ESLs is typically maintained in an ESL data file which contains ESL identification information and ESL merchandise item information. Price information displayed by the ESLs is obtained from a price look-up (PLU) data file. The central server sends messages, including price change messages, to the ESLs through a relay unit which may be mounted in the ceiling of the retail establishment.
The communications link from the relay unit to an ESL, known as the xe2x80x9cdownlinkxe2x80x9d, typically uses radio frequency (RF) technology. To ensure that a message transmitted to the ESL was properly received, the ESL transmits a positive acknowledgement over an xe2x80x9cuplinkxe2x80x9d communication path to the relay, which then relays the acknowledgment to the central server. The downlink communications path is separate from and may employ different technology than the uplink communication path, since the uplink path transmits much less data than the downlink path.
ESLs may be installed in a variety of premises presenting many RF barriers which may hinder the transmission of messages along the downlink. Previously, these barriers to RF transmission were overcome by including additional relay units, each having a single transmit antenna, at multiple locations throughout the retail establishment in order to ensure reliable transmission and coverage. While it is important for the communication links to be reliable, for ESL systems to be cost effective the ESLs must be inexpensive and the cost of the infrastructure, such as the relay units, kept to a minimum. Adding additional relay units to the retail establishments to overcome the RF barriers can significantly increase the cost of an ESL system, as each of the relay units includes a relatively expensive transceiver or transmitter.
Thus, it would be desirable to provide an ESL system having a relay unit which includes a single transmitter connected to multiple transmit antennae to provide improved RF transmission while maintaining lower costs.
The present invention advantageously provides methods and apparatus for a wireless ESL communication system including a relay unit having multiple transmit antennae connected to a single RF transmitter. The transmitter is connected to the multiple transmit antennae through an impedance matched power splitter which uniformly splits the transmitter power output and allows each transmit antennae to transmit a fraction of the total transmit power produced by the transmitter. By locating the transmit antennae in multiple locations in a retail establishment, an improved pattern of RF coverage can be provided for ESLs, when compared to the traditional single transmit antenna. Additionally, the cost of the ESL system is low since fewer RF transmitters are required.
A more complete understanding of the present invention, as well as further features and advantages of the invention, will be apparent from the following detailed description and the accompanying drawings.